1. Field of the Invention
The present invention relates to a method of time-synchronized data transmission in induction type power supply system, particularly to the method of data transmission in power supply system that enables synchronous transmission of power and data signals to prevent mutual interference with noise resistance ability. By using timers installed in microprocessors of a supplying-end module and a receiving-end module and operations of programs, the supplying-end module arranges the time to start detecting trigger signals in advance, adjust power output to make it easy to recognize signals and calibrate and synchronize the timers automatically, and shut off detection to prevent interference with electric load noise when no data is transmitted, thus achieving the function of transmitting data signals stably.
2. Description of the Related Art
In the digital age, digital products are seen everywhere in our life, for example, portable electronic devices such as digital cameras, mobile phones, music players (MP3 and MP4) and etc. These portable electronic devices and products tend to become light, thin, short and small in design. The first requirement for portability is power supply, and the most common solution is to install rechargeable batteries in portable electronic devices, so that these devices can be recharged when electricity runs out. Yet, now everyone has a number of portable electronic devices with a specific charger compatible with each of them. To use a charger for charging a portable electronic device, it is necessary to link the connection interface (plug) of the charger with a receptacle and plug the connector of the charger at the other end into the portable electronic device. While repeated plugging and pulling of connection interfaces easily causes damage to its terminals in the long period, induction type power supply systems can avoid this problem by transmitting power through coil induction without terminal contact.
Usually, functional settings or compilation and transmission of data, etc. shall be conducted for electronic devices in addition to charging. For some electronic devices, settings and input can be conducted directly, but for other electronic devices (e.g. music players (MP3, MP4, etc), digital cameras, electronic watches, portable game machines and consoles), settings cannot be conducted directly and other electronic devices (such as computers, personal digital assistants, etc.) are required to fulfill functional settings and data transmission. Besides, usually charging and data transmission cannot be conducted synchronously and must be carried out separately. Induction type power supply systems (or so-called wireless chargers) currently available in the marketplace rely on two coils to operate: one acting as a supplying-end coil to transmit power and the other acting as a receiving-end coil to receive power. Since wireless power energy can cause dangers and heat up metal objects on the same principle as an induction stove, it is also easy to cause damage or failure of objects that are being charged due to heating effect.
For existing induction type power supply systems, the most important technical problem is the ability to identify objects placed on the supplying-end coil. Like a cooking induction stove, induction power can transmit enormous energy of electromagnetic waves, which may heat up metal objects and cause dangers if directed towards these objects. To solve this problem, some firms try to develop technologies of identifying objects, and after putting efforts for several years, find that the best solution that depends on a receiving-end coil of a receiving-end module to transmit feedback signals and on a supplying-end coil to receive signals. The most important core technology is to achieve the function of transmitting data through the induction coils. It is difficult to transmit data stably through induction coils for supplying power, because main carrier waves are transmitted by high-power electricity and may be affected by interferences occurring during use of power systems. Moreover, since it also constitutes a frequency-changer control system, the operating frequency of carriers will not be fixed; furthermore, when the induction coil is used to supply power, a wireless communication channel (such as infrared, Bluetooth, radio frequency identification (RFID) or WiFi communication channel, etc) is established separately. However, adding wireless communication devices into the existing induction type power supply system will lead to increase of manufacturing cost for the system.
When induction type power coils are used to transmit data, one problem that should be noticed is how to transmit and receive data synchronously. Like the method of transmitting data over RFID, the method of transmitting data over supplying-end coil is operated in the way that the supplying-end coil transmits the main carrier to the receiving-end coil and the receiving-end circuit feeds back by controlling load changes. In existing design of induction type power supply systems, power energy and data are transmitted in unidirectional way, i.e. the power energy (LC main oscillating carrier transmitted from the supplying-end coil) is transmitted from the supplying-end module to the receiving-end module, while the data code is fed from the receiving-end module to the supplying-end module. But the receiving-end module only receives energy that is either strong or weak from the supplying-end module without emitting data signals of communication actively, and can feed back only after getting close to the supplying-end module and receiving power. And the supplying-end module cannot transmit data codes if not supplying power energy, so there are still considerable limitations and inconveniences in use of the induction type power supply system.
Refer to FIGS. 30 and 31, which illustrate the structures of receiving power and data feedback of the receiving-end module. As shown in these figures, there are two types of structural design for this purpose: resistance type and capacitance type. The resistance type modulation of feedback signals originates from the passive RFID technology, which relies on resistance of the receiving-end coil to switch feedback signals to the supplying-end coil for reading, as applied in a wireless charging system disclosed in US Patent Publication No. 20110273138, entitled Wireless Charging System (Taiwan Patent Publication No. 201018042, entitled Wireless Charging System) filed by Access Business Group (Fulton). According to this invention, the load resistor of the switch placed on the rear side of the receiving rectifier, or Rcm in FIG. 31, is used to make changes in impedance characteristics on the receiving-end coil that is fed back to the supplying-end coil. These changes will be analyzed by the detection circuit on the supplying-end coil, and then decoded by the software installed in the processor of the supplying-end module.
Referring to FIGS. 32 and 33, FIG. 32 illustrates the signal status on the supplying-end coil. When the Rcm switch is closed, it will cause the impedance on the receiving-end coil to drop down, making the amplitude on the supplying-end coil increase after feeding back to the supplying-end coil. Then the asynchronous serial format in UART communication mode is used for encoding, i.e. to interpreting logic data codes by determining whether the modulation status changes at this time point in a fixed time cycle. However, this way of encoding may result in a problem that modulation load is kept switching on within a cycle time.
Refer to FIGS. 34 and 35, which illustrate the data transmission format in qi specifications. These figures show a data transmission frequency modulated and demodulated with the 2 KHz timing frequency. It can be worked out that the longest duration of modulation load conduction is a cycle in a signal feedback. In UART communication mode, the duration of modulation load conduction does not affect system functions. In induction type power supply system, however, the state of modulation load conduction will affect the state of power supply, because the main carrier at the supplying-end is used to supply power and can transmit strong current drive force due to the coupling effect of the supplying-end module and receiving-end module. But the resistor load at the receiving-end module needs to withstand feedback drive currents; when power increases, the power to be withstood at Rcm will increase, too. Besides, in the process of modulation, the electric currents that originally go to the receiving-end module for output will be shunted by Rcm, thus reducing the output capability at the receiving-end module. Moreover, signals are easy to recognize only when the cycle time for signal modulation is far less than that of transmission frequency. As main carrier waves in induction type power supply system can only operate at a lower frequency (roughly 100˜200 KHz) as a result of components' performance restraints or in accordance with laws and regulations electromagnetic interference, while data transmission depends on modulation of main carrier waves, the data transmission frequency must be far lower than the main carrier wave frequency to ensure smooth operation. Due to the conflict of the above conditions, when the power of induction type power supply system is increased, data modulation with resistor loads will not work any more.
Since signal modulation loads need to absorb considerably large electric currents and it leads to the problem of power loss following power increases, making it impossible to use this method, some firms propose a new method of capacitive signal modulation. In US Patent Publication No. 20110065398, entitled Universal Demodulation And Modulation For Data Communication In Wireless Power Transfer by Hongkong-based Convenient Power HK Ltd (referring to FIGS. 36 and 37), capacitors and switches are added at the receiving-end module to feed signals to the supplying-end module and generate changes in the voltage, current and input on the supplying-end coil, and data signals are identified through analysis of these three variables of signals. The shortcoming of this method lies in that all three variables are so weak that several amplification circuits are needed for analysis, making the circuit cost increase significantly.
As shown in FIGS. 38, 39, 40, 41 and 42, coil amplitudes or coil output power will increase during signal modulation to enable the analysis circuit to identify the amount of variance and transmit it to the microprocessor for analysis. In the figure of analysis amplification, when the amplitude of the induction type power supply system reaches Point A, it will increase to Point B following signal modulation, and may increase to Point C or D if the modulation energy increases (low resistance is used at Rcm in the previous example). In the induction type power supply system, the amplitude changes with the load state at the receiving-end module. Under the condition of high power output, the amplitude may operate at Point C or D, and may move to Point E if signals are modulated under such circumstance. This can be seen as an overload reaction, and at this time, the power supply system will lose the capability to increase amplitudes through signal modulation to transmit data, which may lead to the system failure. In light of this limitation, the induction type power supply system is designed to make its amplitude reach a lower position of Point A or B with low power output. When the output power is increased, the amplitude needs to be increased to Point C or D, resulting in system failure.
Therefore, to solve this problem, all firms that engage in this field focus on how to increase the power for the induction type power supply system